Machine for smoothing and/or polishing lens faces

ABSTRACT

A machine for smoothing and/or polishing lenses comprising a holder which is carried on a slide. The slide is guided for movement in two mutually perpendicular directions, both of which are perpendicular to a main axis of the machine. The slide is moved in a plane perpendicular to the main axis along a curved path which results from the combination of two orbital motions produced by cams. One cam is secured to the main shaft and rotary motion is transmitted to the other cam by an element which rotates about the axis of the main shaft and is driven from the main shaft through a transmission means which has a velocity differing from unity.

BACKGROUND OF THE INVENTION

This invention relates to a machine for smoothing and/or polishing anon-spherical curved face of a lens, which face has a differentcurvature of different angular positions about an optical axis of thelens. Such a face is referred to herein and in the art as a"cylindrical" face but it will be understood that the term embracesforms which cannot be generated by the rotation about an axis of astraight line which is parallel to that axis.

To smooth and polish a cylindrical lens face, the face is rubbed on alayer of an abrasive on a complementary face of a tool. Relativemovement of respective reference axes of the lens and tool must becontrolled to avoid changing the curvature of the face of the lens andthe relative movement must change throughout the operation to avoid theformation of marks on the face of the lens.

Known machines for smoothing and polishing cylindrical faces of lenseshave complex driving means for moving one of the tool and the lensrelative to the other in a manner such that the locus of a point on thelens relative to a point on the tool shows little regularity. Theseknown driving arrangements cause abrupt changes of direction of the toolor lens and elements of the driving means undergo rapid changes invelocity. These elements must be robust and accordingly are fairlymassive.

During operation, the known machines are subjected to severe vibrationwhich is accompanied by excessive noise and by deterioration of themachine. The inertia of moving parts results in variations between thepressure under which the tool contacts the lens at different places onthe face of the lens and these variations in pressure result in changesin the curvature of the lens face. A further disadvantage of the knownmachines is that the driving means is not capable of controllingrelative movement of the reference axes of the tool and lenssufficiently accurately. Inaccuracy in such control also leads tochanges in the curvature of the lens face.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided amachine for smoothing and/or polishing lenses comprising at least onepair of relatively movable holders arranged for holding respective onesof a tool and the workpiece which are to be rubbed together by relativemovement of the holders, constraining means for maintaining respectivereference axes of the holders parallel to a reference plane and drivingmeans for causing said relative movement of the holders wherein theconstraining means comprises a first slide, means for guiding the firstslide along a first rectilinear path relative to a body of the machine,a second slide and means for guiding the second slide along a secondrectilinear path relative to the first slide, the second path beingtransverse to the first path.

Preferably, said paths are perpendicular to each other.

According to a second aspect of the invention, There is provided amachine for smoothing and/or polishing lenses comprising at least onepair of relatively movable holders arranged for holding respective onesof a tool and a workpiece which are to be rubbed together by relativemovement of the holders, constraining means for maintaining respectivereference axes of the holders parallel to a reference plane and drivingmeans for causing said relative movement of the holders, wherein thedriving means comprises first and second elements which are rotatableabout a main axis at respective different speeds, the first elementdefining an auxiliary axis offset from the main axis to move around themain axis when the first element rotates and an output element mountedfor rotation about the auxiliary axis, the second element being soassociated with the output element as to move the output element aroundthe auxiliary axis when the second element moves around the main axis.

The main axis may be fixed with respect to a body of the machine andthere may be provided means for connecting one of the holders with theoutput element for displacement therewith relative to the main axis. Theother holder may occupy a fixed position with respect to the main axisand the body of the machine.

There may be provided coupling means for coupling the second element tothe output element, the coupling means being adapted for transmittingrotary drive from the second element to the output element and foraccommodating relative displacement of the second element and outputelement radially of the axis about which one of these elements rotates.

The coupling means may comprise a roller which is movable along a slot.

The driving means may include transmission means for transmitting rotarymotion between the first element and the second element with a velocityratio other than unity.

There may be provided a main shaft on which the first element is securedand the transmission means may comprise a lay shaft which is driven fromthe main shaft and from which drive is transmitted to the secondelement.

The lay shaft axis is preferably fixed with respect to the main axis.

BRIEF DESCRIPTION OF THE DRAWINGS

One example of an embodiment of the invention will now be described,with reference to the accompanying drawings, wherein:

FIG. 1 shows diagrammatically a side elevation of a machine forsmoothing and/or polishing a lens face,

FIG. 2 shows diagrammatically a cross section of certain parts of themachine on the line 2-2 of FIG. 1,

FIG. 3 shows diagrammatically a cross section of further parts of themachine on the line 3-3 of FIG. 1,

and

FIG. 4 shows a cross section of the parts shown in FIG. 2 in a planecontaining a main axis of the machine.

DESCRIPTION OF A PREFERRED EMBODIMENT

The machine comprises a body 1 which remains stationary during operationof the machine and may stand on a bench so that the machine is at aconvenient height for loading lenses and tools into the machine. On thebody, there is provided a vice 2 for holding one of a lens and a toolwhich are to be rubbed together. In the particular example shown, asmoothing or polishing tool 3 is clamped in the vice and is held therebyin a fixed position relative to the body 1. The vice can be opened bymeans of a hand wheel 4 for substitution of the tool 3 by a differenttool.

On an upwardly facing convex face of the tool 3, there rests a lens 5having a downwardly facing, concave face which is to be smoothed orpolished. On the surface of the lens remote from the tool, there is ametal pallet 6 to which the lens is secured, for example by pitch or bya low-melting point alloy. In an upwardly facing surface of the pallet6, there are formed two recesses in which there engage a pair of spigots7. The spigots are provided on a lens holder 8 which is supported on oneend of a lever 9 for pivoting movement relative to the lever about ahorizontal axis 10 which extends from front to rear of the machine. Thelens holder may take various known forms, one of which is that of ayoke.

The lever 9 is supported for pivoting about a horizontal axis 11 whichis perpendicular to the axis 10. For urging the lens 5 towards the tool3 and establishing a predetermined pressure at the interface between thelens and tool, there is provided a piston and cylinder unit whereof thepistion 12 is connected through the intermediary of a universal joint 13with an end of the lever 9 remote from the lens holder 8. The cylinder14 of the unit is connected at its end remote from the lever 9 with thebody 1 through the intermediary of a further universal joint 15.

The machine further comprises driving means for causing movement of thelens holder 8 relative to the body 1 and the tool 3 in horizontaldirections to rub the faces of the lens and tool together, anconstraining means for maintaining respective reference axes 16 and 17of the vice 2 and lens holder 8 parallel to a reference plane. Thisreference plane is parallel to the opposed surfaces of the jaws of thevice 2 between which the tool 3 is gripped and contains the referenceaxis of the vice.

The constraining means comprises a set of first slides 18 to 21 and apair of rectilinear bars 22 and 23 for guiding the first slides alongrespective rectilinear paths relative to the body 1. The bars 22 and 23are parallel to each other, are secured to the body 1 and are arrangedwith their lengths extending from front to rear of the machine. Theslides 18 and 19 are slidable along the bar 22 and the bars 20 and 21are slidable along the bar 23.

The constraining means further comprises a second slide 24 and a pair ofrectilinear bars 25 and 26 for guiding the second slide along arectilinear path transverse to the bars 22 and 23. In the particularexample shown, the bars 25 and 26 are perpendicular to the bars 22 and23. Each of these bars is perpendicular to a main axis 27 of the machinewhich extends in the same general direction as that in which the vice 2and lens holder 8 are spaced apart. The bars 25 and 26 are carried bythe first slides 18 to 21 for movement therewith. Opposite end portionsof the bar 25 are secured in respective apertures in the slides 18 and20 and opposite end portions of the bar 26 are secured in respectiveapertures in the slides 19 and 21. The bars 25 and 26 extend throughrespective apertures in the second slide 24 with a sliding fit. Theslide 24 is thus constrained against turning about any axis relative tothe body 1 but is free to undergo limited movement relative to the bodyin all directions perpendicular to the main axis 27.

The pivot by which the lever 9 is supported for pivoting about the axis11 is carried by and is fixed with respect to the second slide 24 sothat the lever 9 can turn relative to the body 1 only about the axis 11and the lens holder 8 can turn relative to the body only about the axes10 and 11 which are perpendicular to each other and to the main axis 27.The lens 5 is constrained against turning about the main axis 27 or anyaxis parallel thereto.

The driving means comprises a main shaft 28 which is supported inbearings 29 on the body 1 for rotation about the main axis 27, thelatter being fixed with respect to the body. For driving the main shaft,there is provided a motor 30 having an output shaft which is connectedwith the main shaft by a belt and pulley drive 31. On the main shaft,there is carried a first element in the form of a cam 32 which is keyedto the shaft for rotation therewith about the main axis 27 and a secondelement in the form of a pulley 33 which is rotatable about the mainaxis 27 independently of the main shaft 28.

The periphery of the cam 32 is eccentric with respect to the main axis27 and defines an auxiliary axis 34 offset from the main axis. An outputelement in the form of a cam 35 is arranged to rotate about theauxiliary axis, running on the periphery of the first cam 32.Preferably, a ball bearing is interposed between the cams 32 and 35 butthis bearing has been omitted from the drawing for clarity ofillustration. For transmitting displacement of the output cam 35 to thesecond slide 24, there is provided a ring 36 which is secured to thesecond slide and runs on the output cam. Again, a ball bearing ispreferably interposed between the cam 35 and the ring 36 but thisbearing has been omitted from the drawing for clarity. The interfacebetween the output cam 35 and the ring 36 is eccentric with respect tothe auxiliary axis 34. Accordingly, if the output cam 35 is turned aboutthe auxiliary axis it causes the ring 36 and the second slide 24 to bedisplaced along a circular path relative to the auxiliary axis.

For turning the output cam 35 about the auxiliary axis, there isprovided transmission means for transmitting rotary motion from the mainshaft 28 to the pulley 33 and coupling means for transmitting thatmotion from the pulley to the output cam. The coupling means couples theoutput cam and pulley 33 together for rotary motion but is adapted toaccommodate relative displacement of the pulley and output cam radiallyof the auxiliary axis 34. In the pulley 33, there is formed a radiallyextending track 50 in which there is engaged a roller 37. The roller iscarried on a spindle 38 secured to the output cam 35. If the pulley isrotated about the main axis 27, the roller 37 is carried around thataxis and so turns the output cam about the auxiliary axis 34, the rollermoving along the track in the pulley towards and away from the auxiliaryaxis to accommodate the eccentricity of the axes.

The transmission means comprises a lay shaft 39 supported by bearings 40on the body 1 for rotation about an axis which is fixed relative to thebody and is parallel to the main axis 27. A belt and pulley drive 42 isprovided for transmitting drive from the main shaft 28 to the lay shaftand a further belt and pulley drive 43 is provided for transmittingrotary drive from the lay shaft to the pulley 33. It will be noted thatthe pulleys of the drives 31, 42 and 43 each rotates about a respectiveaxis which is fixed relative to the body 1 so that there is no variationin the tension of the drive belts during operation of the machine.

The respective velocity ratios of the belt and pulley drives 42 and 43are such that the overall velocity ratio of the transmission meansdiffers from unity. The speed of rotation of the pulley 33 is less thanthat of the first cam 32. We have found that a transmission means havinga velocity ratio of 416:19 gives satisfactory results.

As the main shaft 28 rotates, the auxiliary axis 34 is carried aroundthe main axis 27 by the first cam 32. This motion is transmitted throughthe output cam 35 to the ring 36 and the second slide 24. An additional,but slower, rotary motion is applied to the ring 36 and slide 24 byrotation of the output cam 35 about the auxiliary axis 34, in the mannerpreviously described. The motion of the slide 24 is therefore theresultant of combining two circular motions of different frequency andthe lens holder 8 executes a corresponding motion relative to the vice2. Because the motion is produced by combining continuous rotarymotions, neither any element of the driving means nor the lens 5 issubjected to abrupt changes of direction or rapid changes in velocity.

A further advantage provided by the fundamentally rotary motion producedby the machine described, as compared with the fundamentallyreciprocating motions provided in known machines, is that a greaterdegree of rubbing is produced by a circular motion of given throw thanis produced by a reciprocating motion of the same throw. This enables arelatively small throw to be used in the machine described and thisenables proper contact to be maintained between the lens and tool withrocking of the lens about the axis 10 and rocking of the lens about anaxis defined by the spigots 7 through only relatively small angles.

If a single machine is to be used on different occasions for smoothingand for polishing lenses, then we prefer that the eccentricity of thefirst cam 32 and the eccentricity of the output cam 35 should beadjustable. We have found that good results are achieved if, forsmoothing, the eccentricity of the first cam 32 is 33 mm and theeccentricity of the output cam 35 is 10 mm. For polishing, we have foundthat a first cam with an eccentricity of 57 mm and an output cam with aneccentricity of 10 mm provides good results.

To enable the eccentricity of the first cam 32 to be adjusted, this camis formed in two parts, namely an inner part 44 and an outer part 45.The inner part 44 is keyed to the main shaft 28 and the outer part 45 isreleasably clamped to the inner part by a clamping screw 46. When theclamping screw is slackened, the outer part can be adjusted relative tothe inner part about an axis which is offset from the main axis 27 toadjust the eccentricity of the periphery of the first cam relative tothe main axis.

Similarly, the output cam 35 is formed in two parts, namely a lower part47 and an upper part 48. The lower part 47 runs on the first cam 32 andcarries the spindle 38. The ring 36 runs on the upper part 48 and theparts 47 and 48 are releasably clamped together by a clamping screw 49.When the clamping screw is slackened, the eccentricity of the ring 36with respect to the auxiliary axis 34 can be adjusted. The range ofadjustment of the cams 32 and 35 is limited by the respective forms ofthe components of these cams so that it is not possible to set themachine in a condition in which a moving part of the machine will foulsome other part of the machine during operation.

Industrial applicability:

The driving means and constraining means of the machine combine to causethe lens 5 to move smoothly relative to the tool 3 along a curved pathwhich has no abrupt changes of direction, brings about a relativelylarge amount of rubbing contact between all parts of the lens face andthe tool and controls the relative movement so that the reference axis17 of the lens is maintained in the reference plane containing thereference axis 16 of the tool. Although the machine is especially usefulfor smoothing and polishing cylindrical faces of lenses, both convex andconcave faces, the machine is also useful for smoothing and polishingpart-spherical faces of lenses.

As in known machines for smoothing and polishing lenses, there may beprovided means for feeding a slurry of abrasive particles in a liquidcollant to the interface between the lens 5 and the tool 3 and there mayfurther be provided a housing in which the vice 2, tool 3 lens 5 andlens holder 8 are disposed. Such housing would prevent the abrasiveslurry being thrown away from the machine and would enable the slurry tobe collected and re-used in a known manner. Since the housing and slurryfeed means form no part of the present invention, they have been omittedfrom the accompanying drawings and will not be more particularlydescribed.

I claim:
 1. A machine for smoothing and/or polishing lenses comprisingat least one pair of relatively movable holders arranged for holdingrespective ones of a tool and a workpiece which are to be rubbedtogether by relative movement of the holders, constraining means formaintaining respective reference axes of the holders parallel to areference plane and driving means for causing said relative movement ofthe holders characterised in that the driving means comprises first andsecond elements which are rotatable about a main axis at respectivedifferent speeds, the first element defining an auxiliary axis offsetfrom the main axis to move around the main axis when the first elementrotates and an output element mounted for rotation about the auxiliaryaxis, the second element being so associated with the output element asto move the output element around the auxiliary axis when the secondelement moves around the main axis.
 2. A machine according to claim 1further characterised in that the main axis is fixed with respect to abody of the machine and there is provided means connecting one of theholders with the output element for displacement therewith relative tothe main axis.
 3. A machine according to claim 1 or claim 2 furthercharacterised by means for coupling the second element to the outputelement, the coupling means being adapted for transmitting rotary drivefrom the second element to the output element and for accommodatingrelative displacement of the second element and the output elementradially of the auxiliary axis.
 4. A machine according to claim 3further characterised in that the coupling means comprises a rollermovable along a slot.
 5. A machine according to claim 2 furthercharacterised by the provision of transmission means for transmittingrotary motion from the first element to the second element with avelocity ratio differing from unity.
 6. A machine according to claim 5further characterised by a main shaft on which the first element issecured and by a lay shaft comprised by the transmission means, therebeing provided first drive means for transmitting rotary drive from themain shaft to the lay shaft and second drive means for transmittingrotary drive from the lay shaft to the second element.
 7. A machineaccording to claim 6 further characterised in that the lay shaft issupported by bearings for rotation about an axis which is fixed withrespect to the axis of the main shaft.
 8. A machine according to claim 1or claim 2 further characterised in that the constraining meanscomprises a first slide, means for guiding the first slide along a firstrectilinear path relative to the body of the machine, a second slide andmeans for guiding the second slide along a second rectilinear pathrelative to the first slide, the second path being transverse to thefirst path.
 9. A machine according to claim 8 further characterised inthat said first and second paths are each perpendicular to the mainaxis.
 10. A machine according to claim 1 wherein the main axis and theauxiliary axis are substantially parallel.